Streams API for PHP Extension Authors

Note:

The functions in this chapter are for use in the PHP source code and
are not PHP functions. Information on userland stream functions can be found in the
Stream Reference.

Overview

The PHP Streams API introduces a unified approach to the handling of
files and sockets in PHP extension. Using a single API with standard
functions for common operations, the streams API allows your extension
to access files, sockets, URLs, memory and script-defined objects.
Streams is a run-time extensible API that allows dynamically loaded
modules (and scripts!) to register new streams.

The aim of the Streams API is to make it comfortable for developers to
open files, URLs and other streamable data sources with a unified API
that is easy to understand. The API is more or less based on the ANSI
C stdio family of functions (with identical semantics for most of the main
functions), so C programmers will have a feeling of familiarity with streams.

The streams API operates on a couple of different levels: at the base level,
the API defines php_stream objects to represent streamable data sources.
On a slightly higher level, the API defines php_stream_wrapper objects
which "wrap" around the lower level API to provide support for retrieving
data and meta-data from URLs. An additional context
parameter, accepted by most stream creation functions, is passed to the
wrapper's stream_opener method to fine-tune the behavior
of the wrapper.

Any stream, once opened, can also have any number of filters
applied to it, which process data as it is read from/written to the stream.

Streams can be cast (converted) into other types of file-handles, so that they
can be used with third-party libraries without a great deal of trouble. This
allows those libraries to access data directly from URL sources. If your
system has the fopencookie() or
funopen() function, you can even
pass any PHP stream to any library that uses ANSI stdio!

Streams Basics

Using streams is very much like using ANSI stdio functions. The main
difference is in how you obtain the stream handle to begin with.
In most cases, you will use php_stream_open_wrapper()
to obtain the stream handle. This function works very much like fopen,
as can be seen from the example below:

The table below shows the Streams equivalents of the more common ANSI stdio functions.
Unless noted otherwise, the semantics of the functions are identical.

ANSI stdio equivalent functions in the Streams API

ANSI Stdio Function

PHP Streams Function

Notes

fopen

php_stream_open_wrapper

Streams includes additional parameters

fclose

php_stream_close

fgets

php_stream_gets

fread

php_stream_read

The nmemb parameter is assumed to have a value of 1, so the prototype looks more like read(2)

fwrite

php_stream_write

The nmemb parameter is assumed to have a value of 1, so the prototype looks more like write(2)

fseek

php_stream_seek

ftell

php_stream_tell

rewind

php_stream_rewind

feof

php_stream_eof

fgetc

php_stream_getc

fputc

php_stream_putc

fflush

php_stream_flush

puts

php_stream_puts

Same semantics as puts, NOT fputs

fstat

php_stream_stat

Streams has a richer stat structure

Streams as Resources

All streams are registered as resources when they are created. This ensures
that they will be properly cleaned up even if there is some fatal error.
All of the filesystem functions in PHP operate on streams resources - that
means that your extensions can accept regular PHP file pointers as
parameters to, and return streams from their functions.
The streams API makes this process as painless as possible:

Example #2 How to accept a stream as a parameter

PHP_FUNCTION(example_write_hello)
{
zval *zstream;
php_stream *stream;
if (FAILURE == zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "r", &zstream))
return;
php_stream_from_zval(stream, &zstream);
/* you can now use the stream. However, you do not "own" the
stream, the script does. That means you MUST NOT close the
stream, because it will cause PHP to crash! */
php_stream_write(stream, "hello\n");
RETURN_TRUE();
}

Example #3 How to return a stream from a function

PHP_FUNCTION(example_open_php_home_page)
{
php_stream *stream;
stream = php_stream_open_wrapper("http://www.php.net", "rb", REPORT_ERRORS, NULL);
php_stream_to_zval(stream, return_value);
/* after this point, the stream is "owned" by the script.
If you close it now, you will crash PHP! */
}

Since streams are automatically cleaned up, it's tempting to think that we can get
away with being sloppy programmers and not bother to close the streams when we
are done with them. Although such an approach might work, it is not a good idea
for a number of reasons: streams hold locks on system resources while they are
open, so leaving a file open after you have finished with it could prevent other
processes from accessing it. If a script deals with a large number of files,
the accumulation of the resources used, both in terms of memory and the
sheer number of open files, can cause web server requests to fail. Sounds
bad, doesn't it? The streams API includes some magic that helps you to
keep your code clean - if a stream is not closed by your code when it should
be, you will find some helpful debugging information in you web server error
log.

Note:
Always use a debug build of PHP when developing an extension
(--enable-debug
when running configure), as a lot of
effort has been made to warn you about memory and stream leaks.

In some cases, it is useful to keep a stream open for the duration of a request,
to act as a log or trace file for example. Writing the code to safely clean up
such a stream is not difficult, but it's several lines of code that are not
strictly needed. To save yourself the trouble of writing the code, you
can mark a stream as being OK for auto cleanup. What this means is
that the streams API will not emit a warning when it is time to auto-cleanup
a stream. To do this, you can use php_stream_auto_cleanup().

Streams open options

These constants affect the operation of stream factory functions.

IGNORE_PATH

This is the default option for streams; it requests that the include_path is
not to be searched for the requested file.

USE_PATH

Requests that the include_path is to be searched for the requested file.

IGNORE_URL

Requests that registered URL wrappers are to be ignored when opening the
stream. Other non-URL wrappers will be taken into consideration when
decoding the path. There is no opposite form for this flag; the streams
API will use all registered wrappers by default.

IGNORE_URL_WIN

On Windows systems, this is equivalent to IGNORE_URL.
On all other systems, this flag has no effect.

ENFORCE_SAFE_MODE

Requests that the underlying stream implementation perform safe_mode
checks on the file before opening the file. Omitting this flag will skip
safe_mode checks and allow opening of any file that the PHP process
has rights to access.

REPORT_ERRORS

If this flag is set, and there was an error during the opening of the file
or URL, the streams API will call the php_error function for you. This
is useful because the path may contain username/password information
that should not be displayed in the browser output (it would be a
security risk to do so). When the streams API raises the error, it first
strips username/password information from the path, making the error
message safe to display in the browser.

STREAM_MUST_SEEK

This flag is useful when your extension really must be able to randomly
seek around in a stream. Some streams may not be seekable in their
native form, so this flag asks the streams API to check to see if the
stream does support seeking. If it does not, it will copy the stream
into temporary storage (which may be a temporary file or a memory
stream) which does support seeking.
Please note that this flag is not useful when you want to seek the
stream and write to it, because the stream you are accessing might
not be bound to the actual resource you requested.

Note:
If the requested resource is network based, this flag will cause the
opener to block until the whole contents have been downloaded.

STREAM_WILL_CAST

If your extension is using a third-party library that expects a FILE* or
file descriptor, you can use this flag to request the streams API to
open the resource but avoid buffering. You can then use
php_stream_cast() to retrieve the FILE* or
file descriptor that the library requires.
The is particularly useful when accessing HTTP URLs where the start
of the actual stream data is found after an indeterminate offset into
the stream.
Since this option disables buffering at the streams API level, you
may experience lower performance when using streams functions
on the stream; this is deemed acceptable because you have told
streams that you will be using the functions to match the underlying
stream implementation.
Only use this option when you are sure you need it.